The psychological reasons why we want what we can't have — and why we chase someone who pulls away

Sometimes it can feel like you're always chasing something you can't have.

It can feel like the more someone pulls away, the more you end up wanting them.

This is partly due to our vanity and self-esteem, and partly due to our warped sense of their value.

In reality, their perceived value is all in your head, and you're better off pursuing people who actually respect you enough to be honest.

It's easier said than done, though.

"Too often, the thing you want most is the one thing you can't have," said Meredith Grey in the show "Grey's Anatomy." "Desire leaves us heartbroken, it wears us out. Desire can wreck your life."

This will sound all too familiar for people who always seem to be chasing things they can't have. It might be a dream job, or it could be a person — either way, when something is out of reach, they want it that much more.

You might have started dating someone, and thought things were going well. You were attracted to each other, and you were under every impression things were progressing in the right direction. Then they started to pull away, and instead of letting them go, you started bombarding them with messages and calls.

You could feel them slipping further away, but you couldn't control that burning desire to fix whatever went wrong. Predictably, the more they distance themselves, the more you chase them, until eventually they're gone for good.

We place more perceived value on people who are busy

"The less someone responds or reciprocates to one's advances, the more perceived value the pursuer thinks this person has," she said. "So we try harder since this person must really be 'worth it' if he or she is in such high demand — in other words, this person is a scarce resource."

If someone is busy, our minds can go into overdrive thinking they must be spending time with other people. They're obviously popular, so something primal in our brain can make us think they are more valuable than they really are.

In fact, Ettin said that often this means we start to place more value on the other person than we do ourselves. But if someone isn't being honest with you, she said, they simply aren't worth your time,

"This person's lack of response, though, should not imply a higher value," she said. "Rather, at its simplest, it should imply a lack of proper communication... or just rudeness."

Unfortunately, walking away is much easier said than done. When we like someone, our brain will release the hormone dopamine when they appear in our messages, or ask to see us.

We can get hooked on this happy hormone, and start chasing the high, like a drug. If we get intermittent attention from someone, it's all the more addictive than if we got it all the time.

We are susceptible to 'breadcrumbing'

"Our brains love the unpredictability because the highs are higher than if we got the desired reward all the time," Ettin said. "This is why breadcrumbing has sadly entered our lexicon recently."

Thanks to the dopamine, we let people treat us this way, because the reward feels so good on the rare occasions we get it.

"With the extra dopamine, though, comes added anxiety," she said. "'When is he going to text?' 'I haven't heard from her in three days, and I know she's back from her weekend trip by now.' 'If he wants to go out this weekend, he needs to ask since it's already Friday afternoon.' Is that a worthwhile trade-off? I say no."

It can be incredibly tempting to fall for the thrill of the chase, particularly because our vanity can drive us to keep pursuing someone who just isn't interested. But if you can pull yourself away, and devote your time and energy to what you do have rather than what you don't, you're likely to save yourself a lot of heartache in the end.